In March 2023, Google transitioned to Material Design v3 for Google Docs, Slides, and Sheets.

Amongst many things, this change also removed the "Last edit was ______ ago" text in the menubar.

This userscript is an improved version of this one (from here) that works in Firefox.

Not tested on Chrome.

https://greasyfork.org/en/scripts/462209-restore-revision-time-visual-text-in-google-apps is set up to automatically pull from this repo (using webhooks) to update.